The objective of this research project is to establish the molecular basis of the interactions between phospholipids and between phospholipids and cholesterol. The study will utilize aqueous dispersions of lipid vesicles in which the components are organized in bimolecular lamellae similar in form to the organization of these components in biomembranes. The details of the phospholipid- phospholipid and phospholipid-cholesterol interactions will be established by systematic studies involving analytical ultracenrifugation, molecular sieve chromatography, spectrofluorimetry, and proton magnetic resonance spectroscopy. Since the association of phospholipids and cholesterol are important in maintaining the organization and function of biomembranes as well as plasma lipoproteins, the information obtained by this proposal will be an integral part of the developing basis for the rational treatment of disorders arising from abnormalities in both biomembrane and lipoprotein structure.